Xenopus tropicalis primitive myeloid marker expression analysis by RT-PCR and WMISH. (A-F) spib, spi1, cebpa, mpo, mmp7, and globin single embryo qRT-PCR and ventral views of WMISH at stages 18 and 23. Among the transcription factors, (A) spib is the first to be specifically expressed in primitive myeloid cells, (B) followed by spi1. (C) Earlier expression of cebpa is due to its broad mesodermal expression before its restriction to the aVBI. (D) mpo is a neutrophil marker; (E) mmp7, a macrophage marker; and (F) globin, a erythroid marker. Error bars represent the SD of at least 3 independent experiments.